This invention relates to a position sensing apparatus for an object to be measured, which utilizes ultrasonic waves. An object of the invention is to provide a position sensing apparatus which is simple in construction and sensible with a high accuracy with respect to the sensing of the position of a bore which is small in diameter or a groove which is small in width.
The conventional position sensing apparatus for an object to be measured includes apparatus allowing an ultrasonic wave transmit-receive element to rotary-scan with respect to the object so as to sense its position and posture through the intensity of the signal obtained by scanning. Next, an explanation will be given on the outline of the conventional apparatus.
FIG. 1 is a schematic block diagram of the conventional apparatus and FIG. 2 is a perspective view of form sensing by use of the conventional apparatus. In FIG. 1, when a high voltage pulse 17 as shown in FIG. 3 is applied to the ultrasonic wave transmit-receive element 1 shown in FIG. 1, an ultrasonic pulse of the predetermined frequency is sent into the atmosphere, the ultrasonic pulse being reflected by an object 13 as shown in FIG. 2. The reflected signals from the sides 14, 15 and 16 at the object 13 reach the ultrasonic wave transmit-receive element 1 and are amplified by a received signal amplifier 3 and thereafter analog to digital converted by A/D converter 4 so to be stored in a memory 5. FIG. 3 is a waveform chart of a wave of the ultrasonic wave transmit-receive element 1 stored in the memory 5, in which reference numerals 37, 38 and 39 designate reflected signals from the sides 14, 15 and 16 of the object 13 respectively. The reflected signals stored in the memory 5 are transferred to a compact electronic computer 6, by which the propagation times 40, 41 and 42 of reflected signals 37, 38 and 39 shown in FIG. 3 and the reflected signal intensities 43, 44 and 45, are sensed.
In FIG. 2, the ultrasonic wave transmit-receive element 1 is adapted to be fed a control signal from the compact electronic computer 6 and rotary-scanned in the direction of the arrows A and B through a pulse motor driver 11 and a pulse motor 10, thereby moving in steps at a predetermined angle to sense the propagation time and intensity of reflected signal between the element 1 and the object 13 to be measured. FIG. 4 plots the reflected signal intensity from the object 13 to be measured when the ultrasonic wave transmit-receive element 1 rotary-scans, in which the abscissa axis represents an angle of rotation of the ultrasonic wave transmit-receive element and the ordinate axis represents the intensity of the reflected signals. Reference numerals 46, 47 and 48 designate reflected signals in arrangement from the sides 14, 15 and 16 of the object 13 to be measured respectively, so that the directions of the sides 14, 15 and 16 are sensed from the rotary scanning angle of the ultrasonic wave transmit-receive element when an angle of the reflected signal becomes its maximum. Since a distance between the ultrasonic wave transmit-receive element 1 and each side 14, 15 or 16 of the object 13 is obtainable from the propagation time of the aforesaid reflected signal, the coordinates of sides 13, 14 and 15 of the object 13 are obtainable to thereby enable sensing of the position and posture of object 13 to be measured.
The conventional position sensing apparatus, however, when applied to the form sensing of a bore or a groove, can sense the form of a bore which is larger in width, but for a bore which is small in diameter or a groove which is small in width, the signals reflected from the sides of the bore or groove are superposed on each other, thereby having created a problem in that unless the attenuation for the ultrasonic wave transmit-receive element is greatly improved, the position and posture of object 13 to be measured are impossible to be sensed.